Increase in pop up ads using Safari 13.1
In the last two months (Dec 2021-Jan 2022) I've seen an increase in pop up ads, from zero to every time I use Safari, by way of opening a new browser window. You can see the address form in the Safari window. Sometimes the ad opens, sometimes the address disappears before the ad opens. I've even seen an ad saying Apple has detected unusual pop up activity, and I should click on a link to contact Apple support. I have not done that. My Mac is 6 years old. I'm using high sierra 10.13. Do I have reasonable options to prevent the pop ups?
Thank you.
iMac 21.5″, macOS 10.13